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Cloud seeding

2.
Background
• IPC started evaluating cloud seeding based on a shareowner
inquiry in 1993
• Literature review – 1993 - 1994
• Data collection -1995 (climatology and background silver levels)
• One year program in winter 1996-97
• Operational program started in late winter 2003
• Included two year assessment

5.
Precipitation…
• A given column of air has a limited amount of water vapor it can
hold
• For precipitation to occur, the air column must be at or near
saturation (i.e. relative humidity ≈ 100%)
• Relative humidity is a function of temperature (warm air can hold
more water vapor than cold air)
• However, saturation alone does not lead to precipitation
• Ice nuclei are required for water vapor to convert to ice crystals
• Ice nuclei are found naturally in the atmosphere, but may be
limited relative to available water vapor
• This limitation can provide an opportunity….

7.
Atmospheric Water
Vapor
• There is a lot more water
vapor in the atmosphere
than we can see.
• Not all water vapor is
visible as clouds.

8.
Cloud Seeding
The key is super cooled liquid water…
Water that is in a vapor state, but below freezing.

9.
Cloud Seeding
• Cloud seeding provides mother nature with ice nuclei
• But, it is only effective when ice nuclei are limiting and nature is
performing the other required precipitation processes
– cloud seeding doesn’t create clouds to seed – it will not cure a drought!
• Effectiveness depends on:
– temperatures,
– available water vapor,
– ice nuclei properties,
– cloud droplet and natural ice distributions
• Several agents can be used as ice nuclei, with silver iodide (AgI)
being the most common used in commercial cloud seeding.

10.
Cloud Seeding
Where did it get started?
• In 1946 at GE labs in Schenectady, NY, it was discovered that
various materials can initiate the formation and growth of water
droplets and ice crystals (leading to cloud seeding).
Building on those early discoveries,
• Cloud seeding is conducted in over 40 countries
• Numerous projects in US, including some dating to the 1950’s

26.
IPC’s Dual Tracer
Assessment
Approach (cont.)
• Following seeding, sample snowpack for evaluation of trace levels
of silver, indium, and cesium as well as snowpack density
• Ratio of silver to tracer (ex. Indium) in the snow pack gives an
indication of how much silver deposited by ice nucleating vs.
scavenging processes.

30.
Targeting from
Chemistry Data
• Targeting of the seeding
operations was assessed by
integrating the silver found in
the snow over a given storm
period to estimate the total
amount of silver deposited
during the storm.
December 6 through 9, 2004
March 5 and 6, 2004
Control
site
MC
BC
NG
V MM
KR BM
MC
BC
NG
V MM
KR BM
CM
Ground-generator Site
= silver
deposited
100 x 10 -12 g
= silver 100 g
released
Example Targeting Maps for the March
2004 and December 2004 storm periods

31.
Aircraft Targeting
• Aircraft seeding identified
by using a cesium tracer.
• Identification of aircraft
tracer was complicated by
dust – cesium, which was
also deposited in the snow .
Aircraft
Cesium
Cesium
from dust
2D profile of snow cesium

32.
Targeting Results
• The amount of silver deposited downwind of active ground
generators was much greater than that found at the control sites.
• Silver deposition maps show that the center of the target area was
affected by the seeding operations.
• Indium concentrations were generally very low
– Silver not from scavenging
• Evidence for targeting by aircraft was found in the center of the
target area in December 2004.
• The project layout and operations can effectively hit the target area
with both ground generators and aircraft.
• Determining precipitation increases…

40.
Trace Chemistry
Summary
• Due to compaction of the snow pack, water increases could not be
estimated for the 2003-2004 season.
• During 2004-2005, DRI concluded cloud seeding revealed an
average increase of 7%. Individual storm events ranged between
7 and 35% increases.
• Under favorable conditions, greater increases may be obtained
through longer seeding periods.
• Moving to flares significantly increases seeding potential from the
aircraft.

41.
How do others view
cloud seeding?
• During California energy crisis while PG&E was facing
bankruptcy, the CA PUC advised PG&E that they would continue
their cloud seeding programs during reorganization.
• PG&E is working to expand their project

42.
Idaho Power’s Cloud
Seeding Project
• At the request of shareholders – began investigating cloud seeding in 1993
• Literature review 1993 and 1994
• Climatology study water year 1994-95
• Contracted operational program in 1996-97
• Planned to perform internal program in 1997-98
– canceled do to no mechanism to recover project expenses and share benefits
• Reinstated in Feb 2003.
• Operational including assessment in fall of 2003
• Completed second year of assessment and third year of operations in May 2005.
• Currently in final stages of 5th operational year

43.
Idaho Power’s Cloud
Seeding Project
IPC views cloud seeding as a long-term water management tool.
Project Organization
• In literature review, found expert opinions that some commercial
programs benefit public relations more than anything else.
• Most long-term programs have an in-house component -
representing stakeholders interest.
• Rather than commission entire project, IPC elected to employ key
personnel to represent the Company’s interest.
• A 3rd party provides aircraft and conducted an assessment.

46.
Both Airborne and
Ground-based
• Seeding intended to enhance
snowpack at the higher elevations
above 4500’
• Target area ~ 938 sq. miles
• ~ 497 mi2 above the 6000’ level
• Combined approach provides
more opportunities for addressing
storms.
• Complementary
Too warm for ground, can still fly,
too cold to fly, can still use the
ground units, or,
Use both at the same time